1. Field of the Invention
The present invention relates to an image printing method and image forming apparatus, in which an image is formed with use of a liquid developer, more particularly, to an image printing method and image printing apparatus for which operational conditioning is easily and simply adjusted so that an image formed by an electrophotography technology is transferred successfully.
2. Related Art
From the standpoint of developers used, electrophotography technologies are classified into those of dry development using a solid developer and those of wet (liquid) development using a liquid developer. In conventional electrophotography technologies, wet development is believed to be disadvantageous practically because of some substantial problems, and consequently, the field of image formation by electrophotography technologies has been long occupied substantially by dry development.
However, electrophotography of wet development has also an advantage which can not be realized by dry development. Specifically illustrated are: since an extremely fine toner of sub-micron size can be used, high image quality can be realized; since sufficient image concentration is obtained with a small amount of toner, an economical merit is obtained and texture corresponding to offset printing or other like printing can be realized; since a toner can be fixed to paper at relatively lower temperature, energy saving and high speed output can be realized: and the like. Based on these facts, in recent years, the value of electrophotography based on wet development has been reviewed and development is in progress aiming at practical use.
In a wet mode image printing apparatus, visible images developed on a photosensitive body contains a surplus mount of carrier solvent. Therefore, removal of as much surplus carries as possible before transfer is a significant problem for obtaining good transferred images.
U.S. Pat. No. 4,259,006, Japanese Patent Application Publication No. 4-46426 and Japanese Patent Application Laid-Open (JP-A) No. 4-1774 disclose methods of removing off surplus carriers. In these methods, a surplus amount of carrier solvent on developed images is scraped off by a squeeze roller and blade placed adjacent to or in contact with a photosensitive body, then, a remaining surplus developer is further dried by blow of air. However, practically, if drying of a developed image is insufficient, a remaining solvent tends to cause disturbance in a transferred image, and transfer failure also occurs frequently. Inversely, if drying progresses too much, transfer failure still tends to occur frequently, namely, optimization of the dry condition of developed images before transfer is not easy. Particularly, if the thickness of a toner layer of a developer is large, disturbance of a transferred image and transfer failure tend to occur, Also in the suggestion of the above-described publication, such problems remain unsolved.
On the other hand, Japanese Patent Application Laid-Open (JP-A) No. 10-10874 discloses an apparatus equipped with a spray nozzle for supplying a solvent again to images after drying, as shown in FIG. 1. In this apparatus, an electrostatic latent image formed by an electrostatic charger 2 and an exposing apparatus 3 on a photosensitive drum 1 is developed using a development roller 8, then, a remaining solvent is scraped off by a squeeze roller 9, and a toner is fixed by a set roller 10, then, dried by drying means 12. The dried toner image receives spraying with a solvent 23 transported from a solvent tank 22 to a spray nozzle 21, then, is transferred onto a transfer material 7 by a transfer roller 11 at transfer position 5.
However, the above-described method has a disadvantage that the printing apparatus becomes complicated and large for incorporating the measures for supplying a solvent before transfer. Further, since the amount of aggulomerated developer (toner) on a developed image differs depending on the tone and concentration of an image to be formed, the developed image naturally has a local difference in the amount of the aggulomerated toner which occurs depending on what image is developed. Accordingly, also the amount a solvent evaporated from a developed image and the degree of drying the developed image varies locally depending on the image. Therefore, if a solvent in amount suitable for a thick developed image which is liable to cause excessive drying is fed over the whole region of the developed image, it leads to excess feeding for other thinner images. Namely, it is difficult to prevent, over the whole image region, the excess amount of a solvent from being fed, as compared with the amount of a solvent dried and removed from the image. Consequently, on developed images once revealed excess drying, it is difficult to make the dried condition suitable for transfer over the whole developed image region by feeding of a solvent as in the above-described publication.
As described above, in the conventional wet electrophotography image formation, there is no practical means for grasping the dried condition of a developed image on a photosensitive body, and it is therefore difficult to effect suitable removal of a surplus carrier solvent necessary for attaining good transfer, and a problem occurs that decrease in transfer efficiency due to disturbance of a transferred image and transfer failure is caused.
With these problems in mind, therefore, it is the primary object of the present invention to provide a novel electrophotography image forming method and an apparatus which can control the motion of an image forming system so that an image is transferred under dry condition suitable for transfer, in order to realize constant good transfer.
Another object of the present invention is to provide an electrophotography image forming method and an apparatus which detect condition suitable for transfer by measuring an element useful as a criterion for the condition of an image, can control drying operation based on this condition, and can realize good transfer property and image output of high image quality.
In order to achive the above-mentioned object, a method of printing an image on a print medium with a liquid developer which comprises a liquid carrier and a toner dispersed in the liquid carrier, according to the present invention, comprises: forming a toner image probably containing the liquid carrier, from the liquid developer; removing the liquid carrier from the toner image; transferring the toner image to the print medium; projecting light radiation on the toner image to be transferred, to measure the optical reflection from the toner image to be transferred; and estimating transfer suitability of the toner image to be transferred, by means of the measured optical reflection from the toner image to be transferred, for appropriately controlling the extent of the removing of the liquid carrier.
A printing apparatus for printing an image onto a print medium with use of a liquid developer which contains a liquid carrier and a toner being dispersed in the liquid carrier, according to the present invention, comprises: an image forming system which forms a toner image probably containing the liquid carrier, from the liquid developer: a carrier remover which removes the liquid carrier from the toner image, the carrier remover being controllable to change the extent of removing the liquid carrier; a transfer member which transfers the toner image from the image forming system to the print medium; and an optical instrument which projects light radiation on the toner image to be transferred and measures the optical reflection from the toner image to be transferred, in order to appropriately control the carrier remover.